This invention relates to a register access control device for use in an information processing system connected to a utilization device which is typically a graphic or pattern drawing device.
In the manner which will later be described more in detail, a register access control device is connected in an information processing system to a central processing unit (CPU) of the information processing system through a first bus and comprises a register group connected to the first bus so as to be accessed by the central processing unit. In the register access control device, a command executing unit is connected to the register group and to a second bus which is connected, in turn, to the utilization device. In order to put the command executing unit in operation of supplying result commands and result parameters to the utilization device, the central processing unit accesses the register group to store input commands and input parameters in the register group as stored commands and stored parameters, respectively.
A conventional register access control device comprises a busy/idle indicator connected to the first bus and to the command executing unit. The busy/idle indicator indicates a busy state and an idle state of the command executing unit when the command executing unit is put into operation of referring to and using the register group in executing the stored commands on the stored parameters to produce the result commands and the result parameters and when the command executing unit finishes execution of each of the stored commands. When the busy/idle indicator indicates the busy state, the central processing unit is inhibited to access the register group. Meanwhile, the command executing unit continues its operation. When the busy/idle indicator indicates the idle state, the central processing unit is allowed to access the register group. In the meantime, the command executing unit is kept out of operation. The central processing unit is also kept out of operation insofar as storage of the input commands and the input parameters in the register group is concerned.
When the graphic drawing device is used as the utilization device, the central processing unit may deal with graphic or pattern drawing or computer aided design (CAD). The central processing unit may furthermore deal with information processing as an element of the information processing system. Overall performance of the information processing system and the graphic drawing device is raised by parallel operation or pipeline operation of the graphic drawing or the computer aided design and the information processing.
On making the graphic drawing device draw graphics or patterns, the central processing unit first supplies the register group, as the input parameters, with parameters for use in specifying, for example, positions of points used in the graphics and kinds of lines used in the graphics. Next, the central processing unit supplies the register group, as one of the input commands, with a command for use in drawing either a line segment or an arc of the graphics. Based on such parameters and commands stored in the register group as the stored parameters and the stored command or commands, the command executing unit produces the result parameters and the result commands to make the graphic drawing device draw the graphics.
If at least one of the stored commands and the stored parameters were changed while the command executing unit is dealing with the stored commands and parameters, the command executing device would not correctly produce the result command and parameters. The busy/idle indicator consequently prevents the central processing unit from storing the input commands and parameters in the register group and from changing the stored commands and parameters while the busy/idle indicator indicates the busy state. The central processing unit is kept in a waiting state with respect to access to the register group. The command executing unit is also kept in its waiting state.
In the manner described above in connection with a conventional register access control device, the central processing unit and the command executing unit have been kept in a long waiting time on optimally putting a graphic drawing device or a like utilization device in operation. In other words, a long execution time has been inevitable on duly putting such a utilization device in operation. Merits of the parallel operation have adversely been affected.